1. Field of the Invention
The present invention relates to certain pyrazolo[4,3-c]pyridine compounds, which modulate the activity of protein kinases. The compounds of this invention are therefore useful in treating diseases caused by dysregulated protein kinase activity. The present invention also provides methods for preparing these compounds, pharmaceutical compositions comprising these compounds, and methods of treating diseases utilizing pharmaceutical compositions comprising these compounds.
2. Discussion of the Background
The insulin-like growth factor 1 receptor (IGF-1R, IGF1R) is a member of the insulin receptor subfamily of receptor tyrosine kinases (RTKs). IGF-1R mature protein consists of two alpha chains, which are extracellular and contain ligand-binding function, and two beta chains, which span the cell membrane and contain the intracellular kinase domains. This disulphide-linked (alpha/beta) 2 heterodimer complex is able to bind and be activated by the ligands insulin-like growth factor-1 and -2 (IGF-1 and IGF-2), two circulating growth factors which are believed to mediate many of the effects of Growth Hormone (GH), and which have important physiological roles in foetal and post-natal growth and metabolism. Extracellular ligand binding to IGF-1R results in intracellular tyrosine kinase activation, and like several other RTKs such as the EGF and PDGF receptors, the activated receptor has potent mitogenic, motogenic and anti-apoptotic activity in a wide range of cell types: notably, it directly activates at least two major cell signalling pathways, the ras/MAPK pathway, through recruitment of SHC, and the PI-3 kinase/AKT(PKB) pathway, through recruitment and phosphorylation of the IRS adapter proteins. There is much evidence, both at preclinical and clinical levels, linking increased IGF-1R signalling to development and progression of cancer. This evidence includes observation that IGF-1R is able to induce cellular transformation, that fibroblasts from animals lacking IGF-1R through genetic ablation are extremely resistant to the transforming activity of a wide range of oncogenes, and that IGFs are potent anti-apoptotic agents. Studies of interference with receptor activity through various approaches have demonstrated that inhibition of IGF-1R dependent signalling can result in single agent antitumor activity, and in the enhancement of the activity of a wide range of chemotherapeutic agents and radiotherapy in human tumor cells cultured in vitro, as well as in animal models of disease, including human tumor xenograft models. Such IGF-1R inhibition strategies have included cellular transfection with dominant negative IGF-1R constructs or antisense oligonucleotides, use of IGF binding antagonists and blocking monoclonal antibodies directed against the extracellular receptor, and, significantly, selective small molecule inhibitors of IGF-1R kinase activity. Additional indication that IGF-1R signalling contributes to development of cancer, and thus that inhibition of this receptor may represent a valuable therapeutic option, is provided by the observation that high circulating levels of IGF-1 in human are associated with increased lifetime risk of developing several tumor types, including breast, colorectal, prostate and ovarian cancers, and with poor outcome in multiple myeloma. Importantly, gene and protein expression studies performed on clinical samples have revealed that IGF-1R and its ligands are frequently expressed in a wide range of human tumors. For an overview of IGFs and IGF-1R signalling, physiological function, and detailed description of the evidence supporting involvement of this system in human cancer that is summarised above, as well as in other pathologies, the reader is directed to the many reviews on the subject and references contained therein, for example Baserga R., Hongo A., Rubini M., Prisco M. and Valentinis B. Biochim Biophys Acta vol. 1332 pages F105-F126, 1997; Khandwala H. M., McCutcheon I. E., Flyvbjerg A. and Friend K. E. Endocr Rev vol. 21, pages 215-44, 2000; Le Roith D., Bondy C., Yakar S., Liu J. L. and Butler A. Endocr Rev vol. 22, pages 53-74, 2001; Valentinis B., and Baserga R. Mol Pathol vol. 54, pages 133-7, 2001; Wang Y. and Sun Y., Curr Cancer Drug Targets vol. 2 pages 191-207, 2002, Laron, Z. J Clin Endocrinol Metab vol. 89, pages 1031-1044, 2004; Hofmann F and Garcia-Echeverria C. Drug Discov Today vol. 10, pages 1041-7, 2005.